This invention relates to the use of at least one oxygen-fuel burner in the roof of a glass melting furnace to boost production capacity or maintain current production capacity with either reduction of electro-boost or as a result of deterioration of existing heat recovery equipment such as recuperators or regenerators. The process involves the replacement of a portion of existing or previously existing air-fuel or electrical energy capacity with oxy-fuel energy. With the exception of end-fired regenerative furnaces and electric furnaces the process involves the blocking of regenerative ports or isolation of recuperative burners. In particular the design selection, angling and positioning of the burners over the raw batch materials entering the furnace improves the rate of melting, increase product yield, better energy efficiency and improve glass quality. Accurate control of the stoichiometric ratio of combustion in the burner, rich lean interaction of burners and furnace zonal fuel/oxygen staging are used to optimise heat transfer while minimizing oxides of nitrogen and sulfur dioxide emissions.
Regenerative, recuperative, electric and direct fired furnaces have been commonly involved in the manufacture of glass and related frit products.
Air-fuel regenerative furnaces fall into two categories: cross-fired and end-fired. Cross-fired regenerative furnaces have multiple ports typically three to eight on each side of the furnace that connect to either a common or compartmentalized regenerator to preheat the combustion air. The regenerators which come in various shapes and sizes reverse every 15-30 minutes dependent on furnace operation. During each reversal cycle combustion air from a fan passing through one passage in the reversal valve enters the base of the regenerator on one side of the furnace and is preheated prior to entering the ports which connect to the furnace. Fuel in the form of oil and/or gas is injected either, under, over, through or side of port to produce a flame which is combusted in the glass melting furnace. The hot products of combustion exit the furnace through the opposing side port, down through the regenerator checker bricks releasing heat and then exiting to the exhaust stack through a second passageway in the reversal valve. As the air-side regenerator cools, the exhaust regenerator heats until the reversal valve reverses and combustion air enters the previously hot exhaust regenerator.
The glass is melted partly due to the radiation of the air-fuel flame but mainly from re-radiation from the roof and walls which are heated by the products of combustion. To obtain higher furnace glass production capacity, many furnaces use electric boost by means of electrodes immersed in the glass. This is costly and can cause damage to the glass contact tank walls. Through time, regenerators can start to block due to thermal/structural damage and/or carry-over of raw glass forming materials, also known as batch materials or batch, or condensation of volatile species released from the glass batch. As the regenerators start to block or fail, the preheat temperature of the air in the furnace will reduce. Because of the increased pressure drop, the exhaust side will limit the removal of exhaust gases and therefore limit energy input into the furnace thus reducing furnace glass production.
To recover production capacity lost to preceding regenerator issues or to increase production in a non-encumbered furnace, oxygen has been used by four means: general air enrichment with oxygen, specific oxygen lancing under the port flames, installation of an oxy-fuel burner between first port and charging end wall, and water-cooled oxy-fuel burners installed through the port. The capacity increases from these technologies is limited by access, process requirements or refractory temperature limits.
The End-Fired Regenerative furnace is similar in operation to a cross-fired furnace, however, has only two ports in the end wall which connect to individual regenerators. Regenerator deterioration is the same mechanism as in cross-fired furnaces and similarly electric and oxygen boost is utilized.
To recover production capacity lost to the aforementioned regenerator issues or to increase production, oxygen has been used by three means: general air enrichment with oxygen, specific oxygen lancing under the port and installation of oxy-fuel burners through the furnace side walls down tank. These technologies are typically limited on capacity because of location and concerns for overheating of the furnace.
The recuperative furnace utilizes at least one recuperator type heat exchanger. Unlike the regenerator, the recuperator is continuous with hot concurrent flow heat exchanger where exhaust gases preheat combustion air which is ducted to individual air fuel burners along the sides of the furnace. Recuperative furnaces can also use electric boost. As with regenerative furnaces, recuperators can start to lose their efficiency and ability to preheat the air. They can become blocked or develop holes.
To recover production capacity lost from the aforementioned recuperator issues or to increase production, oxygen has been used by three means: general air enrichment with oxygen, specific oxygen lancing under the air fuel burners and installation of oxy-fuel burners either through the furnace side or end walls. These technologies are typically limited on capacity because of location restrictions and concerns for overheating of the furnace.
Direct fired furnaces do not utilize preheated air and are therefore less efficient than the preceding examples of furnace design. To improve thermal efficiency or increase production capacity, side wall oxy-fuel burners have replaced air fuel burners.
Electric furnaces or furnaces which utilize electricity for majority of melting are typically costly to operate and are subject to a shorter campaign life than the typical fossil fuel furnaces. Once designed it is difficult to increase the production capacity. This invention relates to hot top and warm top electric furnaces and is not applied to cold top furnaces
U.S. Pat. No. 5,139,558 to Lauwers discloses the use of a high-momentum roof-mounted auxiliary oxygen fired burner in a glass melting furnace which is directed to the interface of the melted and solid glass forming ingredients whereby the solid glass forming ingredients are mechanically prevented from escaping the melting zone.
U.S. Pat. No. 3,337,324 to Cable discloses a process for melting batch material in a glass furnace using a burner positioned to fire substantially down over the feed end of a water-cooled furnace.
Co-pending U.S. patent application Ser. No. 08/992,136 discloses the use of roof-mounted burners as the primary source of heat in a glass melting furnace having no regenerators or recuperators.
Briefly, according to this present invention, glass melting furnaces of all designs can be boosted using at least one roof-mounted oxygen fuel burners positioned over the raw batch materials as the materials enter the furnace to improve the rate of melting and improve glass quality and/or glass product yield. Because of the increased rate and yield of the glass melting generated by the design and positioning of these burners, depending on furnace condition and type, at least one or more of the following can be achieved: increased glass production, improved glass quality, reduction in electric boost, recovery of production lost due to inefficient heat recovery (i.e., blocked regenerators), reduction of oxygen use by replacing oxygen enrichment of the furnace atmosphere, reduction of oxygen use by replacing oxygen lancing, reduction of oxygen use by replacing conventional oxy-fuel burners positioned through the walls of a glass furnace, increased furnace campaign life, improved energy efficiency, reduction in emissions of oxides of nitrogen and oxides of sulfur, reduction in fossil fuel usage, reduction in cullet and increased product glass yield.
This invention may be applied to the following types of furnaces. In hot top electric furnace applications of this invention, at least one oxygen-fuel burner will be mounted in the roof of the furnace. In cross-fired regenerative furnace applications of this invention may necessitate at least one pair of the opposing ports to be fully or partially blocked or isolated. In end-fired regenerative furnace applications of this invention, at least one oxygen-fuel burner will be mounted in the roof of the furnace and the combustion air flow reduced by a portion of the original design maximum flow. In all recuperative furnace applications of this invention, at least one oxygen-fuel burner will be mounted in the roof of the furnace. In multi-burner furnaces, burners adjacent to the roof mounted burners should be removed and the air supply isolated. In single burner or single port applications the combustion air flow will be reduced by a portion of the original design maximum flow.
In all direct fired furnace applications of this invention, at least one oxygen-fuel burner will be mounted in the roof of the furnace. In multi-burner furnaces, burners adjacent to the roof mounted burners should be removed and the air supply discontinued. In single burner or single port applications, the combustion air flow will be reduced by a portion of the original design maximum flow.
In all the above cases the scope of the invention is effectively the same: glass melting which was previously performed by air-fuel or oxy-fuel including but not exclusive of furnaces that utilize electric boost or conventional oxygen boosting methods, is replaced by roof-mounted oxy-fuel burners positioned over the raw batch materials entering the furnace to improve the rate of melting and/or improve glass quality and/or glass product yield. Because of the ability to position these burners at specific locations, increased heat transfer to the unmelted raw batch materials is achieved.
In all cases at least one roof-mounted oxy-fuel burner is positioned over the raw batch materials entering the furnace to improve the rate of melting and improvement in quality is utilized and in all multi-port and multi-burner air fuel applications at least one pair of ports or pair of burners are isolated. In all single port and single burner applications the air and fuel are reduced to a portion below the maximum design. The more efficient roof mounted burners provide energy to replace the conventional energy removed from the process and the additional energy to achieve the desired process requirements. The positioning of the burners over the raw batch entering the furnace improves the rate of melting. The stoichiometric ratios and control of the roof-mounted burners and remaining air-fuel burners is critical to minimizing the emission of nitrous oxide and sulfur dioxide.